A colonel from a rebel faction confirmed to Reuters news agency that there were battles going on on the outskirts. Fighters from a Turkish-backed rebel force have joined the defence, he said.

The Syria crisis: Five questions, answered

How did the war start?

The country descended into war after President Bashar al-Assad’s government used deadly force to crackdown on pro-democracy protesters, who took to the streets in March 2011 demanding political freedom.

Who is fighting who?

That’s complicated: President Assad’s regime is fighting rebel groups ranging from pro-democracy groups to jihadist extremists, while a number of foreign powers are providing support to various sides.

How many people have died?

It is not known exactly, as death tolls vary according to the source, but it is estimated to stand at more than 500,000 dead or missing.

How many refugees are there?

More than 5.6 million people have fled Syria since 2011, with another 6.6 million internally displaced, according to the United Nations.

What has happened to President Assad?

His position looked tenuous at one point during the eight year conflict, but thanks to international allies like Russia and Iran, President Assad has won back control of most of Syria, and has set his sights on Idlib.